This proposal is for an investigation of primary visual cortex in macaque monkeys as a visual image processing area, rather than as a passive filter of visual patterns. This project will include studies of linear and nonlinear neural mechanisms of signal processing in V1. The ultimate goals is progress in understanding the function of the cerebral cortex in normal and abnormal visual performance. Research Topics. First, the nature of cortical simple cells as apparently linear spatial processing elements will be studied by measuring spatial phase dependence of the response to contrast reversal gratings as a function of contrast, to test the push-pull model of simple cells in macaque cortex. Then, we will continue our previous research on complex cell responses to so-called "illusory contours" as a way of understanding image segmentation mechanisms. In order to characterize the receptive field organization of cortical neurons that respond to illusory contours, we will determine dependence of IC response on spatial parameters. Low luminance contrast and equiluminant color inducers will be used, to isolate Magno and Parvo inputs respectively. We also aim to measure cross correlation between neurons located along a contour, and investigate whether the presence of the contour or some distinguished feature like corner or angle influences the degree of coherence between neurons. Next, we will study the receptive field properties of V1 hypercomplex (end-stopped) cells quantitatively so that the emergence of the hypercomplex property may be understood mechanistically. These studies lead to investigations of nonlinear image processing in the response to moving visual patterns. We will study the responses of V1 neurons to plaids and other 2-D patterns and compare these responses to 1-D patterns like gratings and edges, in particular looking for spatial, contrast, color, and temporal differences and similarities between the mechanisms that signal 1-D and 2-D motion in V1.